edit: Fedora it is then!
He will be running the AMD 9800 X3D w/ RX 9070 XT, B850 motherboard.
I am deciding between either Fedora (probably KDE) and Bazzite (also KDE), but I’m not sure whether an atomic distro would be better/worse for a newbie.
As far as I understand, atomic distros can be easily rolled back after an update, but you are unable to use apt/dnf/etx, you need to use Flatpak, I think. Would that be limiting for the average user? Also, does Bazzite have better driver support for newer AMD hardware compared to Fedora?


Mint is based on Ubuntu, which has a Hardware Enablement Stack offering newer kernels. I would expect that (or maybe something Mint-specific) to take care of it.
I still would never recommend a “stable release” or LTS distro because the vast majority of security vulnerabilities never receive a CVE, and as a result the a large amount of vulnerabilities go unpatched for months. Also I like distros that take security seriously (Fedora and openSUSE).
Usually they backport security fixes to the stable version.
As I mentioned, most security vulnerabilities are not reported because it may not seem security related. The distro maintainers can’t keep up with every package and read all the commits, so as a result security fixes often go unfocused. It is a real big problem that many security researchers acknowledged.